Rubus pollen are in monads, trizonocolporate, mainly spheroidal, rare ellipsoidal, small- or medium-sized, which range from 13 to 40 µm in diameter (Fig. 1–3, 5). Composed apertures includes meridional directed, long, narrow colpi with mean length 17–34 µm and clear ori on equator ranged from 1 to 5 µm. Apocolpium are 2–9 µm, mesocolpium differ from 11 to 23 µm. There are many deviated grain forms in apertural number (from one to six) and their disposition (Fig. 5). Exine is thin, mean thickness 1.15–1.87 µm, tectate, columellate with striate or striate-perforate ornamentation. The morphological and morphometric characters of pollen of investigated taxa given in Table 2.
Table 2
Pollen morphological and morphometrical characteristics of studied Rubus specimens
Species and number specimen | Polar axis (P), µm; min-max | Equatorial diameter (E), µm; min-max | P / E | Deviated form, % | Apocolpium, µm; min-max | Mesocolpium, µm; min-max | Colpi length, µm; min-max | Ori width, µm; min-max | Exine thickness, µm; min-max | Ornamentation, its features |
1. Rubus idaeus | 19.82 ± 0.86 18.32–20.89 | 18.33 ± 1.21 17.26–20.34 | 1.08 ± 0.57 0.90–1.21 | 0 | 3.34 ± 0.96 2.42–4.77 | 16.37 ± 1.51 13.72–19.04 | 19.73 ± 2.02 16.48–20.24 | 1.0 ± 0.54 0.82–2.49 | 1.49 ± 0.25 0.91–1.83 | Striate-perforate, striae short, smoth, with curls; 1–3 rows of perforations between striae on the distance 0.2–0.8 µm |
2. R. arme-niacus | 18.36 ± 1.36 17.36–20.85 | 15.91 ± 1.90 13.00-19.51 | 1.15 ± 0.23 0.89–1.34 | 9 | 3.04 ± 0.98 2.78–4.56 | 12.06 ± 2.25 9.8 -14.91 | 18.00 ± 1.18 17.13–20.56 | 2.01 ± 1.02 1.28–3.75 | 1.37 ± 0.22 1.07–1.87 | Striate-perforate, striae long, protruding, with curls; 1–4 rows of perforations between striae on the distance 0.2–1.5 µm |
3. R. ulmifolius | 27.25 ± 4.39 23.4–33.7 | 25.26 ± 3.73 20.6–29.4 | 1.08 ± 0.27 0.91–1.34 | 48 | 6.33 ± 1.96 2.97–9.1 | 20.2 ± 3.62 15.08–26.04 | 24.07 ± 5.28 19.39–25.12 | 1.49 ± 0.33 1.2–1.7 | 2.99 ± 1.03 1.9–4.2 | Striate-perforate, striae long, protruding; 1 row of perforations between striae on the distance 0.1–0.2 µm |
4a. R. ibericus | 27.56 ± 2.31 25.26–31.41 | 23.26 ± 2.85 19.31–27.24 | 1.18 ± 0.35 0.93–1.63 | 2 | 5.42 ± 1.46 3.69–7.97 | 16.16 ± 3.05 10.98–20.46 | 28.25 ± 3.2 27.52–30.33 | 3.23 ± 0.82 2.46–4.58 | 1.33 ± 0.33 0.98–1.83 | Striate-perforate, striae long, protruding; 1, rare 2 rows of perforations between striae on the distance 0.1–0.2 µm |
4b. | 29.24 ± 2.91 22.88–34.37 | 24.09 ± 3.93 18.89–31.60 | 1.21 ± 0.38 0.95–1.43 | 3 | 4.31 ± 1.08 3.03–6.05 | 11.35 ± 2.66 8.34–14.28 | 23.71 ± 2.87 18.31–28.05 | 4.78 ± 2.66 2.24–9.78 | 1.76 ± 0.44 0.96–2.71 | Striate-perforate, striae long,protruding; 1, rare 2 rows of perforations between striae on the distance 0.1–0.3 µm |
5a. R. Sanc-tus | 17.88 ± 1.18 15.18–18.68 | 19.04 ± 1.91 14.90-23.44 | 0.94 ± 0.38 0.80–1.25 | 7 | 5.29 ± 1.11 3.38–6.89 | 17.22 ± 1.81 14.32–21.02 | 17.7 ± 1.19 15.92–20.33 | 2.74 ± 0.30 2.23–2.95 | 1.15 ± 0.22 0.75–1.46 | Striate-perforate, striae long, protruding; 1, rarely 2 rows of perforations between striae on the distance 0.1–0.2 µm |
5b. | 24.9 ± 1.56 22.89–26.78 | 21.60 ± 3.17 17.08 25.61 | 1.15 ± 0.17 0.89–1.34 | < 1, sporadic | 4.52 ± 2.38 1.9–8.06 | 15.53 ± 3.7 10.1 -21.04 | 24.06 ± 1.8 22.09–26.04 | 1.67 ± 0.55 1.03–2.29 | 1.32 ± 0.23 0.98–1.69 | Striate-perforate, striae long, protru ding; 1 up to 6 or more rows of perforations between striae on the distance 0.2–1.5 µm |
5c. | 18.64 ± 1.23 17.1–21.3 | 16.99 ± 2.68 12.77–21.24 | 1.09 ± 0.30 0.88–1.45 | 48 | 3.85 ± 1.4 1.91-7.0 | 15.56 ± 2.65 11.28–21.05 | 17.83 ± 2.01 16.68–20.89 | 1.74 ± 0.57 1.10–2.38 | 1.30 ± 0.22 0.98–1.69 | Striate-perforate, striae long, protruding; 1 up to 6 or more rows of perforations between striae on the distance 0.2–1.5 µm |
5d. | 28.85 ± 2.05 25.12–32.22 | 24.52 ± 3.21 19.97–30.24 | 1.17 ± 0.32 0.83–1.32 | 8 | 5.16 ± 1.09 3.82–6.17 | 14.73 ± 2.25 12.23–19.07 | 23.08 ± 1.63 20.02–25.47 | 2.78 ± 0.86 1.19–4.20 | 1.71 ± 0.47 0.86–2.14 | Striate or striate-perforate, striae long, protruding; 0 or 1 row of perforations between striae on the distance 0-0.3 µm |
5e. | 26.98 ± 1.61 25.10-30.97 | 23.35 ± 2.60 18.67–28.19 | 1.16 ± 0.32 0.89–1.33 | < 1, sporadic | 5.46 ± 1.57 2.59–8.06 | 17.06 ± 2.12 12.13–20.88 | 26.25 ± 1.87 24.53–30.86 | 3.13 ± 0.90 1.73–4.57 | 1.36 ± 0.36 0.88–1.91 | Striate-perforate, striae long, protruding; 1–6 rows of perforations between striae on the distance 0.2–1.3 µm |
6. R. fortis | 30.26 ± 2.77 26.14–36.12 | 25.50 ± 4.73 17.37–36.20 | 1.19 ± 0.51 1.42–1.02 | 7 | 6.33 ± 1.14 4.62–8.64 | 22.65 ± 2.85 16.07–27.08 | 25.33 ± 2.32 20.35–29.25 | 2.87 ± 1.38 0.95–6.34 | 1.39 ± 0.38 0.71–2.03 | Striate or striate-perforate, striae long, protruding;1, rarely 2 rows of perforations between striae on the distance up to 0.3 µm |
7. R. dolichol-carpus | 14.87 ± 3.47 12.10–17.40 | 15.61 ± 1.36 13.30-18.52 | 0.95 ± 0.21 0.77–1.31 | 0 | 3.44 ± 1.07 1.91–5.39 | 12.12 ± 2.46 8.83–16.17 | 15.33 ± 2.32 11.35–19.25 | 1.45 ± 0.27 1.33–1.74 | 1.33 ± 0.29 0.75–1.63 | Striate-perforate, striae long, protruding; 1–3 rows of perforations between striae on the distance 0.1–0.6 µm |
8. R. raddenus | 27.4 ± 1.97 23.54–30.24 | 20.77 ± .1.59 17.43 23.98 | 1.32 ± 0.23 0.98–1.57 | < 1, sporadic | 4.25 ± 1.15 2.28–7.25 | 16.46 ± 1.93 12.09–18.36 | 25.41 ± 2.36 23.42–30.5 | 2.15 ± 0.70 1.11–3.40 | 1.37 ± 0.26 0.91–1.84 | Striate-perforate, striae long, protruding; 1–4 or more rows of perforations between striae on the distance 0.2–1.5 µm |
9. R. persicus | 22.42 ± 1.89 19.67–25.63 | 22.19 ± 1.52 20.19-26.00 | 1.01 ± 0.18 0.76–1.16 | 25 | 5.88 ± 0.92 4.07–7.89 | 16.01 ± 3.03 8.3 -18.95 | 21.52 ± 2.79 18.5 -25.36 | 2.27 ± 1.29 1.23–3.95 | 1.35 ± 0.28 0.93–2.04 | Striate or striate-perforate, striae long, protruding; 0–1 row of perforations between striae on the distance 0-0.2 µm |
10a. R. hyrcanus | 31.35 ± 2.66 27.07–34.75 | 29.10 ± 2.89 26.53–34.81 | 1.08 ± 0.17 0.78–1.31 | 10 | 5.71 ± 0.63 4.75–6.83 | 20.38 ± 2.7 17.3–25.2 | 30.65 ± 2.94 28.31–33.7 | 2.22 ± 0.48 1.28–2.98 | 1.35 ± 0.37 0.82–1.73 | Striate-perforate, striae long, proruding; 1–3 rows of perforations between striae on the distance 0.2-1.0 µm |
10b. | 32.90 ± 2.81 27.61–37.18 | 28.92 ± 3.51 19.55–34.49 | 1.14 ± 0.39 0.80–1.28 | 4 | 5.25 ± 1.32 3.58–7.91 | 15.81 ± 2.7 12.01–21.78 | 25.79 ± 2.62 22.09–30.18 | 3.46 ± 1.09 2.12–6.522 | 1.73 ± 0.23 1.21–2.04 | Striate-perforate, striae long, protruding; with curls, 1–4 rows of perforations between striae on the distance 0.2-1.0 µm |
11. R. canescens | 24.29 ± 1.13 22.10-25.79 | 21.97 ± 1.34 18.91–23.92 | 1.13 ± 0.15 0.92–1.36 | < 1, sporadic | 5.19 ± 0.79 3.58–7.91 | 15.81 ± 2.7 12.01–21.78 | 18.79 ± 1.72 15.41–21.95 | 2.87 ± 0.65 1.56–4.06 | 1.39 ± 0.22 1.10–1.66 | Striate-perforate, striae long, protruding; 1 (rare 2–3) rows of perforations between striae on the distance 0.2-1.0 µm |
12a. R. caucasi-cus | 31.06 ± 2.82 27.32–35.66 | 26.58 ± 4.10 18.38–32.89 | 1.17 ± 0.39 0.83–1.49 | < 1, sporadic | 5.54 ± 0.90 4.59–6.83 | 16.62 ± 4.14 9.8 -20.95 | 23.99 ± 2.52 20.54–27.88 | 4.78 ± 2.66 2.24–7.63 | 1.64 ± 0.33 1.06–2.19 | Striate-perforate, striae long, protruding; 1 (rare 2) rows of perforations between striae on the distance 0.2-1.0 µm |
12b. | 32.15 ± 3.37 29.02–33.78 | 25.57 ± 3.62 16.58–30.63 | 1.25 ± 0.41 0.95–1.75 | 0 | 4.68 ± 1.01 2.66–6.05 | 13.17 ± 3.0 9.36–19.89 | 25.24 ± 2.58 21.14–31.35 | 2.88 ± 1.31 1.19–6.34 | 1.87 ± 0.34 1.39–2.39 | Striate-perforate, striae long, protruding; 1 (rare 2) rows of perforations between striae on the distance 0.2-1.0 µm |
13a. R. hirtus | 35.29 ± 2.33 31.71–40.12 | 29.06 ± 2.64 26.13–33.48 | 1.21 ± 0.21 0.94–1.53 | 0 | 6.6 ± 1.6 4.75–9.59 | 21.15 ± 4.25 12.43–25.99 | 34.59 ± 2.24 31.87–39.21 | 1.83 ± 0.67 0.78–2.74 | 1.32 ± 0.19 1.03–1.57 | Striate, striae long, protruding; rare 1 row of perforations |
13b. | 22.01 ± 0.77 20.85–22.95 | 20.64 ± 1.93 17.45–23.89 | 1.07 ± 0.17 0.87–1.31 | 0 | 5.4 ± 1.61 2.86–8.91 | 18.37 ± 2.57 13.73–22.66 | 22.96 ± 1.43 20.24–25.39 | 2.58 ± 0.73 1.47–4.22 | 1.43 ± 0.29 0.91–1.84 | Striate-perforate, striae long, protruding; 1–4 rows of perforations between striae on the distance 0.2-1.0 µm |
14a. R. caesius | 26.85 ± 0.85 25.48–27.99 | 22.48 ± 1.37 20.31–24.07 | 1.19 ± 0.55 1.06–1.38 | 3 | 5.52 ± 1.13 3.84–8.77 | 17.57 ± 2.38 13.79–22.57 | 27.62 ± 2.33 24.05–42.41 | 2.69 ± 0.97 1.65–4.11 | 1.36 ± 0.17 1.11–1.65 | Striate-perforate, striae long, pro truding; 1–4 rows of perforations between striae on the distance 0.1–0.5 µm |
14b. | 32.64 ± 1.87 27.21–34.58 | 33.60 ± 1.58 29.40-36.25 | 0.97 ± 0.14 0.75–1.18 | < 1, sporadic | 7.47 ± 2.19 4.42–9.89 | 22.2 ± 1.93 18.5 -26.38 | 26.63 ± 2.56 23.6-30.94 | 4.56 ± 2.28 1.90–8.82 | 1.61 ± 0.57 0.86–2.19 | Striate-perforate, striae long, protruding; 1–6 rows of perforations between striae on the distance 0.3–1.5 µm |
15. R. saxatilis | 20.05 ± 1.18 18.56–21.46 | 18.87 ± 1.70 17.43 22.92 | 1.09 ± 0.13 0.81–1.23 | 0 | 5.49 ± 1.67 2.9–8.37 | 16.78 ± 2.95 12.82–21.85 | 18.92 ± 1.92 16.95–21.33 | 1.69 ± 0.47 1.10–2.23 | 1.39 ± 0.18 1.07–1.47 | Striate-perforate, striae long, protruding, with curls; 1–2 rows of perforations between striae on the distance 0.1–0.3 µm |
Pollen shapes, outlines and sizes
The length of polar axis / equatorial diameter ratio (P/E) is around 1.10, varies from 0.75 to 1.75, and according to Erdtman system (1952) pollen shapes may be oblate-spheroidal, spheroidal, prolate-spheroidal, or subprolate. Typically, a pollen polar view is circular (Fig. 1a, q) or may be slightly rounded triangular (Fig. 1m, Fig. 2i, Fig. 5d), or slightly two-three-four-lobate (Fig. 1i). Equatorial view is elliptic or round (Fig. 1–2).
The pollen size varies in different specimens of the same species (Table 2, Fig. 4). There, small grains, which are less than 25 µm in diameter, are found in R. idaeus, R. armeniacus, R. sanctus (5a, 5c), R. doliocarpus, R. hirtus (13b) and R. saxatilis. Small and slightly larger pollen were discovered in R. sanctus (5b), R persicus and R. canescens. Small and medium grains occur in R. ulmifolius, R. ibericus, R. sanctus (5e, 5f), R. hyrcanus (10b), R. raddenus, R. caesius (14a) and medium pollen accouting for more than 25 µm in diameter, in R. fortis, R. hyrcanus (10a), R. caucasicus, R. hirtus, R. caesius (14b). As such, different specimens of the same species may have small- or medium-sized grains,
for example pollen of R. sanctus, R. hyrcanus, R. caesius (Fig. 4a, b). No one subgenus, section, or series differs from other by pollen size. Alternatively, the length of polar axis in specimens 5a and 5c of R. sanctus are less than in 5d and 5e, and length of polar axis of two specimens of R. hirtus (13a, 13b) do not intersect (Fig. 4a). The values of the equatorial diameter of two specimens for each of R. hirtus (13a, 13b) and R. caesius (14a, 14b) do not overlap. (Fig. 4b). Grains about the same size are found in a half of studied specimens (Table 2), while others demonstrate a greater spread, mostly ranging in equatorial diameter (Fig. 4b).
Pollen variability in number of apertures, arrangement and forms
In addition to typical three-colporate pollen, many studied samples (excepting six ones- see Table 2) are characterized by the presence of one, two, four or six colporate grains, as well as various deviating forms. The percentage of deviating grains in the samples varies from zero to 48 (Table 2, Fig. 5). The most diversity was found in specimens from subgenus Rubus series Discolores, up to 48 percent into specimen, and in series Dolichocarpae pollen deviations rich up to 25 percent of studied grains. Other series of subgenus Rubus have none or rare non-typical apertural pollen forms. Pollen heteromorphism in subgenera Idaeobatus and Petrobatus have not defined.
Various and rare atypical forms vary in the number and arrangement of apertures. All detected deviating forms, together with typical ones (i.e. all individual variability), depicted in some standard projection, can be ordered in such a way that they form a network of continuous rows
following a simple and visual geometric pattern (Fig. 6).
In this series, a grain form with a circular aperture on the equator (with symmetry; Fig. 5a, 6a) may be gradually transformed into other regular grain forms with another symmetry (Fig. 6d, i). The deviating less symmetrical shapes turn out to be intermediate forms between them (Fig. 3a, 6c, g, h).
Form with circular aperture bends symmetrically toward both hemispheres of the pollen grain – into a form with an circular aperture twisted like a seam on a tennis ball (Fig. 2f); or into a four-colpate form with separate \/\/-shaped pairwise beveled colpi (Fig. 5f, 6i). The gradual appearance of two additional apertures at the poles of the tennis ball-form transforms it into a six-rugate grain form, with apertures located globally along the edges of the tetrahedron (Fig. 3e-f, 5k-r, 6g-l). There are also transitional deviations to other polyrugate panaperturate forms (Fig. 5s, 6k) and to the four-colpate form, with double meridionally oriented apertures (Fig. 3i, 5i, j, t, u, 6j).
Apertures structure
Apertures are composed and consist of ectoapertures (colpi) and endoapertures (ori). Ectoapertures are represented by meridional oriented narrow long colpi with pointed ends (Fig. 1c, e, j, k, s, 2e, j, k o, 3b-d). In equator over ora, colpi is usually connected by bridge of diverse intensity and completeness in different grains of the same specimens (Fig. 1j, o, s). The most well-marked bridge found in R. idaeus, R. ibericus (4a), R. raddeanus, R persicus, R. hyrcanus (10a), in other specimens or the same individual grains bridges are poorly expressed and sometimes absent. Colpi membranes are granulose (Fig. 1j, k, 2a, c).
Endoapertures (ori) have a width of 0.78 to 4.58 µm, detected under a light microscope (Table 2). Typically, ori are clearly visible, but rarely, for example in R. caesius weakly expressed. The width of ori is diverse, even in one specimen or grain (Fig. 3b, 4c). Often, the ori widen and the shape of ori from the inside often resembles “butterfly wings” (Fig. 3b-d, h).
Exine and ornamentation
Exine is thin, mainly 1.3 µm in thickness (but may differ in thickness from 0.78 up to 2.40 µm), tectate, columellate; three layered envelope compose from tectum, columellate infratectum and underlying layer (including endexine). All three layers are visually equal to each other in thickness (Fig. 3g-j). In the endoaperture zone, exine delaminates and forms a cavity (Fig. 3i, j).
All specimens have variations of striate type of exine ornamentation (Fig. 1–2). SEM investigation show that striae are thin, about 0.2 µm in width, slightly protruding or smoothed, straight or flexuose, meridional oriented and often running from pole to pole, parallel to colpus, sometimes branching or forming curls (Fig. 1d, f, f, h). Usually striae are long with a pronounced relief, but in R. idaeus they are shorter and smoother, with a length from 2 µm (Fig. 1d). The distance between striae varies from zero to 1.0-1.5 µm. The surface differs from striate to striate-perforate (when perforations appear between the stria). Round perforations (0.1–0.2 µm or less in diameter) between striae are located in one or more rows – single, few or numerous perforations (Fig. 1–2). Striate or striate-perforate patterns with from zero to one or rarely two rows of perforations between striae on the distance up to 0.2 µm are found in R. sanctus (5d), R. fortis (Fig. 1j), R. persicus (Fig. 1r) R. caucasicus (Fig. 2h) and R. hirtus (13a) (Fig. 2f). The primary part of specimens have striate-perforate ornamentation with one-three rows of perforations between stria on the distance 0.2–0.8 µm (Fig. 1d, n, 2l, p), but patterns with up to six rows of perforations between stria on the distance up to 1.5 µm occur in some specimens (R. ulmifolicus (Fig. 1f), R. sanctus (5b, 5c) (Fig. 1l), R. raddenus (Fig. 1t), R. hyrcanus (Fig. 1p), R. canescens (Fig. 2b-d).
Overview of pollen ornamentation in Rubus subgenera with species growing in Azerbaijan
We analyzed pollen ornamentation of three subgenera (Online Resource 1), whose representatives grow in Azerbaijan and border areas. These are the subgenera Idaeobatus, Eubatus (Rubus) and Cylactis according to Fokke (1910–1911; 1914). Despite the fact that in the articles the pollen sculptural types of the studied Rubus species can be called differently, after reviewing the factual material, we reduce all the sculptures to three groups (Online Resource 1): 1) typical striate or striate-perforate (not painted, TYPE indicated); 2) non-typical striate types with significant deviations from TYPE, for example, rugulate, with very short striae, or with supertectate verrucae-like structures, or with disconnected (disrupted) muri, or with muri well abobe typical (colored grey); 3) non-striate types, for example, perforate or verrucate (colored green).
Online Resource 1 is presented in tabular form, the species into subgenera were arranged in alphabetical order. The sources of palynomorphological data are indicated after species name. After analyzing the distribution of many Rubus species, we found three main centers of origin and distribution. In the last column with geographical origin, we have highlighted the territories united in these centers. We have left European and Mediterranean (including Asia Minor, the Caucasus and around the Caspian areas) regions uncolored (Europa+); Asian (Central to Southeast) and Malaysian regions are colored in turquoise (Asia+); and the American ones are painted yellow (America). A few species have extensive regions of origin, originating from two or more continents. Pollen data for more than half of the representatives of the most numerous subgenera Idaeobatus and Eubatus (Rubus) and the part of Cylactis members are combined in Online Resource 1. The summarized data are presented in Table 3.
Groups of pollen ornamentation: 1) typical striate or striate-perforate (TYPE); 2) non-typical striate types with significant deviations from TYPE, for example, rugulate, with very short striae, or with supertectate verrucae-like structures, or with disconnected (disrupted) muri, or with muri well abobe typical; 3) non-striate types.